Support for Azure Postgres Cluster

## Background and Motivation

Adding support for Azure Cosmos DB for Postgres Cluster (Citus extension)

see https://learn.microsoft.com/en-us/azure/cosmos-db/postgresql/concepts-cluster

## Proposed API

```diff
namespace Aspire.Hosting;

public static class AzurePostgresExtensions
{
+ public static IResourceBuilder PublishAsAzurePostgresClusterServer(this IResourceBuilder builder, Action, ReaourceModuleConstruct, PostgresSqlClusterServer>? configurrReaource)
}
```

## Usage Examples

## Alternative Designs

## Risks